1. Field of Invention
The present invention relates generally to the field of inspection, and more specifically to apparatus and methods of using same for inspection of materials such as cylindrical and tubular members.
2. Related Art
Inspection of metal pipe or solid tubular members by magnetic means conventionally involves magnetizing the member to create a magnetic field which extends circumferentially and is characterized by lines of magnetic flux which extend either axially of the tubular member or generally perpendicular to its axis, dependent on the manner by which magnetism is induced. In many of the present systems, current flow through a wire coil positioned about the tubular member forms magnetic lines of flux through the opening of the coil which extend axially of the member under inspection. In other systems, current flows axially of the tubular member within the wall thereof so as to create a magnetic field, the lines of flux of which extend circumferentially about the tubular member in an orientation substantially perpendicular to the tubular member. The presence of structural flaws or anomalies in the wall of the tubular member, such as surface nicks or pits, cracks, voids, or various crystalline discontinuities, disturbs the uniformity of a magnetic field in the wall of the tubular member. Accordingly, the structural integrity of the tubular member and its relative freedom of such flaws may be inspected by sensing and detecting the magnetic field variations with sensors disposed closely adjacent the surface of the tubular member.
The sensing of variations in a magnetic field in a pipe wall is customarily achieved by passing or moving an induction coil or similar device through the magnetic field and any magnetic field variations to induce voltages in the coil indicative of the magnetic field variations. The voltages or voltage signals may then be transmitted to appropriate recording and processing equipment. For optimum detection sensitivity and for detection of very small cracks in a pipe wall which can be a few thousandths of an inch in depth, it is necessary that the detecting or sensor coil be placed closely adjacent the exterior surface of the tubular member. Normally the adjacent coil is disposed from 0.002 inches (0.051 mm) to 0.020 inches (0.51 mm) relative the surface of the tubular member with an axis of the coil substantially perpendicular to the surface. The sensor coils are mounted in a support, conventionally referred to as a sensor shoe, which is provided with contact surfaces adapted to contact with the surface of the tubular member in a manner so that the sensing coil is supported closely adjacent the surface of the tubular member at an optimum distance or spacing. Normally, the coil is protected from direct contact with the surface of the pipe by means of a thin shim of magnetically transparent material.
Inspecting the surface of the tubular members requires that the inspection sensor be moved along the surface in a predetermined inspection path. In one widely used pipe inspection apparatus, a plurality of sensor shoes are applied to the surface of the pipe in circumferential spacing thereabout and each of the sensor shoes is moved relatively to the pipe in a circumferential helical path whereby the plurality of sensors provides more than 100 percent coverage of the pipe surface. The relative movement may be effected by moving the sensors longitudinally while rotating the sensor shoes around a stationary pipe or the pipe can be moved longitudinally while the sensors are rotated about the pipe. In any event, there is relative sliding movement between the sensor shoes and the pipe surface, which causes wear of the contact surfaces of a sensor shoe by extensive use. The shim also can come into contact with the pipe and can be similarly eroded. The wearing down of the contact surfaces and shim results in the coils being supported from the pipe surface inside the optimum spacing range or possibly being damaged by eventual contact with the pipe. When either event occurs, a new sensor shoe is required.
Furthermore, sensor shoes are customarily designed for use with a specific diameter of pipe, and the contact surfaces of a sensor shoe are fixed in a permanent orientation such that when placed in contact with the surface of the pipe, the sensing coil is positioned for optimum detection sensitivity. Accordingly, a given sensor shoe is designed for inspection of only one diameter of pipe and is inappropriate for use as an inspection sensor for pipes of a different diameter since for such pipe diameters the sensing coil is supported at other than an optimum distance from the surface to be inspected.
When a typical oil well is drilled, a casing is installed to prevent cave-in, the casing extending from the earth's surface to the bottom of the well. To convey fluid from the formation to the surface, a string of tubing (typically jointed or coiled tubing) is typically run inside the casing. A device referred to as a sucker rod pump may be employed to remove the oil and Sucker rod pumps may be anchored within a lower end of the tubing and the pump reciprocated by means of a string of sucker rods extending from the earth's surface. Sucker rods are typically formed of steel and may be installed by means of couplings that are attached between threaded ends of the rods. A typical sucker rod may, for instance, be of about 25 feet in length with a coupling between each length of rod. The sucker rods reciprocate within tubing which typically may be 2-4 inches in internal diameter. Very few pumped oil wells are perfectly vertical. If an oil well is not perfectly vertical the sucker rods tend to slide against the interior surface of the tubing, and if the couplings are of larger diameter than the sucker rods, vertical reciprocation of sucker rod couplings against the interior surface of tubing may be detrimental both to the coupling and to the tubing itself. Couplings may wear causing the sucker rods to separate, or a hole can be worn in the tubing, with consequential decrease of oil production to the earth's surface. Whipping of sucker rods against the internal surface of the tubing may occur, which may be detrimental to the rods, the rod couplings, and the tubing. For these and other reasons, some operators provide stabilizers on the exterior of sucker rods to prevent excess wear of sucker rod couplings and the interior of the tubing. Currently there is no known apparatus or method for inspecting the sucker rods in terms of cracks or corrosion, except for taking the sucker rods to a shop, which usually requires compete disassembly of the sucker rod string.
The presence of paraffin may be another problem encountered in pumping oil wells. If the paraffin can be maintained in solution in the crude oil, the oil may be pumped without significant problem. However, in cold regions, or in wells wherein the surface temperature is much lower than the downhole temperature, paraffin may solidify on the internal walls of the tubing, and may actually stop flow completely. For this reason, many operators install so-called paraffin scrapers on sucker rods for scraping at intervals equal to or slightly less than the stroke of the pump jack to keep the walls of the tubing from closing in to the point that fluid flow is restricted. There are many scraper designs, but all present the same problem as sucker rod couplings from the standpoint of inspection of the sucker rods. Current inspection methods and apparatus are not adequate for in situ inspection.
From the above it is evident that there is a need in the art for improvements in tubular member inspection methods and apparatus.